make f(x,y,z)=vector make a vector-valued function

[jason]

Currently this makes a vector over callable symbolic expressions: f(x,y,z)=(x^2,y^2,x*z*y). But this doesn't work: f(x,y,z)=vector([x^2,y^2,x*z*y]). This means that it's painful to do calculations on symbolic vectors and easily make new vector valued functions.

[burcin]

How does this relate to #11180?

[kcrisman]

They are related, but different, I think. #11180 is about allow the f in the description to take a vector as an input; this one is about creating a new function using a vector. Best to keep them separate.